A lithium-ion battery comprising a positive electrode containing, as a principal component, a lithium oxide having a layered rock-salt structure and represented by chemical formula: LixM1yM2zO2-d, wherein 1.16≦x≦1.32, 0.33≦y≦0.63, 0.06≦z≦0.50, M1 represents a metal ion selected from Mn, Ti and Zr, or a mixture thereof, and M2 represents a metal ion selected from Fe, Co, Ni and Mn, or a mixture thereof, and a negative electrode containing, as a principal component, a material capable of intercalating/deintercalating lithium ions has been recently expected as a secondary battery having a high energy density. However, this type of lithium-ion battery may have a problem of not stably providing a high capacity.
Patent Literature 1 discloses a technique for improving cycle durability and stably providing a high capacity by an oxidation treatment in which a charge/discharge cycle is repeated within a potential range not exceeding a prescribed potential, for example, a charge/discharge cycle is repeated within a potential range in which the highest potential is not less than 3.9 V and less than 4.6 V relative to the lithium metal counter electrode. In addition, Patent Literature 2 discloses a technique for improving cycle durability and stably providing a high capacity by a charge/discharge pre-treatment (an oxidation treatment) in which a charge/discharge cycle is repeated with a controlled charging capacity (charging electric capacity). Although these oxidation treatments have the effect of allowing the battery to stably provide a high capacity, the effect is still insufficient.